CDL issues...an odd one (1 Viewer)

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Joined
Jul 10, 2004
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Location
Knoxville TN
I'm having some issues out of the center diff lock on my cruiser. It's a 97' w/ 160k miles. I have a CDL switch and the 7 pin mod. This issue is that the center diff locks up just fine when the truck is cool but as soon as I've driven it a while it won't lock at all. It doesn't seem to have anything to do with the outside temp just the temp of the drivetrain.

So, If I jump in the truck after its sat a while and try to lock the diff, it will lock up every time without issue but if I drive it 30 minutes to the trail and try to lock it...no dice. There have been times where I thought it might be locking but the dash light didn't come on so swapped the position sensor with no change. Since the center wont lock (or if it is locked, it's not telling the computer) the axles won't lock. It's really making me crazy...anybody have any ideas? I'm tired of wheeling Subaru style.
 
Sometimes the temperature has an effect on (bad) electrical connections, in the sense that with heat some metal will expand and it's possible for a bad or broken connector to stop making proper contact. Otherwise I can't see a direct link between heat and the ability to lock it.
 
Yeah, I'm thinking electrical as well. I've tried getting under the truck and jiggling wires but the exhaust is right there and I have a slee belly pan which, in addition to transferring heat all around the t-case, makes it tough to reach up there and mess with the wiring. Not being able to diagnose it when it's cool is really complicating things.

Any suggestions on where in the loom or plug to check first?
 
Which "position" sensor have you swapped?

There are 3 switches on the transfer case:

1. L4 position switch - senses that the transfer case has been shifted to low range and initiates the CDL process when in stock configuration. When the pin 7 mod is done that eliminates the CDL activation via the L4 position switch. The CDL switch you have added solely controls the activation of the CDL process.

2. Neutral Position Switch - senses when the transfer case is in the neutral position which has no impact on CDL activation.

3. Center Diff Lock Indicator Switch - senses and confirms when the CDL lock has actually occurred. Without this confirmation the front and rear axle lockers can not be activated.

To solve your issue when hot you need to determine in order:

1. Listen for the CDL control relays in the kick panel to activate when pressing the CDL dash switch. Hear the relays - good, otherwise look at CDL relay control circuits

2. Listen for the whirl of the CDL actuator underneath the truck. Hear the actuator - good, otherwise bad actuator or issues with wires or connectors

3. Disconnect the connection to Center Diff Lock Indicator Switch. Short the pins of the wire side of the connector. The dash CDL and ABS lights should illuminate -good, otherwise look at wiring and connectors

4. Remove Center Diff Lock Indicator Switch and test proper functionality with an ohm meter. Replace or recondition if faulty.

5. Remove CDL actuator, manually operate linkage, make sure everything operates smoothly and dash lights work.
 
The CDL indicator switch is the one I've checked, the other two shouldn't matter. I swapped one from my LX that worked perfectly. The cruiser acted the same and the LX still worked perfectly. The relays click but that's it. I'm pretty sure the motor is good since it works every time when it's cool.
My exhaust is over the frame so there's a lot of heat near that side of the case. I think it's electrical caused by exhaust heat but another scenario that I'm considering, albeit unlikely, is that the case has 80w140 royal purple in it and the heavy oil is causing some issue with the locker when it heats up...80 cool/140 hot...hmmm. The oil has been in it a lot longer than this issue has been going on but then again the exhaust has been there a while too. If neither of these ideas pan out I'll work my way down the list above.
 

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